Float glass (coated or uncoated) is typically soda-lime-silica based, and when coated with an AR coating or the like is susceptible to damage as a result alkalis such as sodium (Na) diffusing outwardly from the glass to the surface and possibly into coatings such as AR coatings or low-E coatings provided on the glass. This leaching or diffusing of sodium outwardly from the glass may take place during heat treatment (HT) such as thermal tempering of the coated article, or over time in environmental conditions. On uncoated glass, the sodium upon reaching the surface may react with water or the like to produce visible stains or smears on the glass surface. Moreover, sodium diffusion into coatings on the glass can damage the coatings thereby leading to defected coated articles.
As an example, in commercial applications such as photovoltaic devices, displays such as LCDs, picture frame, and the like, mono-layer AR coatings are sometimes applied on soda-lime-silica based glass substrates. Sodium ions in the glass over time, especially when subjected to high temperature and humidity conditions such as those used in accelerated aging tests and thermal tempering, migrate to the surface and the resulting increase in alkalinity can cause corrosion on the surface of the coated article. Adverse effects of sodium migration are also known in the display industry where liquid crystal material may become damaged by sodium ions migrated through transparent conductive coatings such as indium tin oxide coatings.
In photovoltaic and other applications, the sodium ions which migrate to the surface of the glass also penetrate into porous coatings of silica or the like, and cause erosion of the coatings which manifests in the form of defects in coatings especially after exposure to high temperatures and/or humidity.
It is known to treat the surface of glass with materials such as aluminum (e.g., see JP 60-176952, and WO 2004/096724 to Hessenkemper, both of which are hereby incorporated herein by reference). However, such treatments are not done in an efficient manner consistent with the manufacture of many coated articles.
In view of the above, it will be apparent that there exists a need in the art for a method of making coated articles having good durability of AR coatings on glass substrates.